The invention relates to a process for the manufacture of an inner shoe for skiing boots by in situ filling the inner shoe with foam, whilst the foot of the wearer, clad with a double walled sock (hollow sock) is placed inside the shoe, the foam material being introduced into the hollow sock in the lower part of the boot and the air displaced thereby being released at the top end thereof.
A process of this nature has become known from U.S. Pat. No. 3,834,044. It offers the advantage that the boot is made to fit accurately the shape of the foot of the wearer. In this context a filling tube positioned in the longitudinal central plane of the boot conducts the foam into a cavity in the heel region from where the foam in the course of its reacting and curing is distributed onwards in an uncontrolled manner towards the front and upper parts of the boot. In the case of skiing boots the inner shoe generally extends above the ankle. The foam, in the course of reacting, first enters into a space of large volume, expands therein and only subsequently thereto the foam travels in an uncontrolled fashion into the upper and the tip region which has a much lesser volume. The air between the inner shoe lining and the outer layer is displaced due to the chemical reaction of the components and escapes to the atmosphere through a venting tube provided in the upper ankle region of the boot. Accordingly, the foam travels in the direction of least resistance. However, the air to be displaced is not discharged fully by way of the venting tube, but also remains trapped, particularly in the tip region, but also in part in the upper inner shoe region and forms air bubbles. The forward supply of not yet reacted foam is delayed by congestive effects. Since the reaction takes place within narrow limits it can happen, due to retardation of the throughflow velocity, that the front regions are not or only inadequately filled with foam. The maintenance of the components temperature in particular, which is one of the factors influencing the reaction period can only be maintained with very great difficult in condition as prevail in the trade. Apart from the aforementioned disadvantages it also happens quite frequently that excess foam enters on one side and may displace the foot in the lower region out of the axis of the skiing boot. The foot will then be displaced either obliquely or parallel to the boot axis and be set in the foam asymmetrically. This situation has an adverse effect when skiing. Finally, when foam is injected from behind, the foot is pushed forward by the reaction pressure onto the Achilles tendon and the heel region. This leads to the further drawback that a spacer toe-cap inserted for the maintenance of the required toe space will result in excessive pain in the toe region during the foam procedure.
It is known from DE-OS No. 24 56 754 that the foam is introduced into the front region of the boot, however such that the foam is not conducted into a hollow sock, but into the cavity between a sock and the inner periphery of the outer boot. The drawback of this procedure is that at the upper end of the boot no opening is provided for the displaced air, a factor which can give rise to airlocks.
In accordance with DE-OS No. 21 06 667 two inlet appertures for the plastics material are provided above the heel region whilst a single outlet apperture is provided on the upper side of the boot tip. This manner of introducing the foam may result in an uneven distribution of the foam and in addition air-bubbles may form in the upper region of the boot because such bubbles tend to rise upwards and can then not escape through the outlet opening in its relatively low position.
OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION
It is an object of the present invention to overcome the drawbacks of the known processes. In this context it is advantageous that the foam material enters the ankle region with comparatively high pressure, so that in this region, where the foot is subjected to the greatest lateral pressure loads, a compact adequate cushioning is created without the formation of dead spaces due to trapped air in the remaining foam-filled regions of the inner shoe. In order to attain this object it is proposed, in a process as set out in the introduction, that in accordance with the invention, the foam or respectively the composition employed for filling the boot with foam is introduced on both sides of the boot in the region between the ankle and the instep.
Due to these expedients the air escapes upwards without forming air-locks. The introduction of the foam in the region between the ankle and the instep provides the advantage that the composition which expands in the heel region where the largest quantity is required, will enter there directly and without detour and forms a compact mass.
Advantageously the foam or the composition is introduced to the right hand and left hand sides of the longitudinal plane of symmetry of the boot. This results in a uniform distribution of the foam.
Advantageously, the two cavities in the front region of the boot into which the foam or the composition is introduced are partitioned from one another. It is advantageous if the foam or the composition is introduced on both sides of the lower end o the entry opening of the boot or in the region of such opening. This results in a further improvement of the flow of the foam. In this context it is of particular advantage if the air escapes on both sides of the longitudinal plane of symmetry of the boot. This produces the effect that the reacting foam causes the air to be pushed forward uniformly on both sides of the boot and to be displaced outwards entirely.
By commencing the foam introduction from the front, the foam is first applied over the naturally narrowest regions and only subsequently thereto the foam is driven into the larger free space or the heel region respectively. The generation of congestions is avoided by the predetermined physically correct direction of flow and only due to this technology can the disadvantage of asymmetrical foam introduction by avoided. Due to the pre-programmed and simultaneous foam introduction into the instep and ball regions and alignment of the foot is maintained and the foot is not displaced axially.
Finally, due to the foam introduction from the front over the foot, no thrust is exercised in the skiing boot axis because the reacting foam slides over the lateral instep region towards the rear and does not encounter attach areas for such thrust. This results in a proper flow around the foot without the foot position being changed. An improved and uniform cushioning is attained by this measure.